U.S. Pat. No. 5,527,508 to Childers et al. discloses a method for enhancing the penetration of vapor sterilants into openings and apertures of complex objects. The patent discloses a method that includes a plurality of sterilant injection phases. During each sterilant injection phase, a predetermined amount of sterilant is injected into a chamber containing articles to be sterilized under vacuum. As a result of the injection of the sterilant, the pressure in the chamber increases to a pressure greater than the initial pressure in the chamber. The sterilant vapor is allowed to distribute itself through the chamber for a period of time. A compression gas is then introduced into the closed chamber in an amount effective to raise the pressure in the chamber to a sub-atmosphere pressure to drive the vapor sterilant into lumens or passageways of the articles to be sterilized.
Conventional sterilization cycles typically employ four of the aforementioned “sterilant injection phases” to effect sterilization of the articles or instruments within the sterilizer.
The method disclosed in the foregoing patent is typically utilized in sterilizers having sterilization chambers dimensioned between 150 cubic feet and 160 cubic feet. (The examples set forth in U.S. Pat. No. 5,527,508 disclose tests conducted in a 154-cubic-foot chamber.)
In recent years, there has been a desire for smaller and smaller sterilizers for sterilizing smaller instruments in shorter periods of time. Small sterilizers, having sterilization chambers of approximately 50 cubic feet, have become desirable for use in medical offices and similar facilities. It was thought that the method disclosed in the aforementioned U.S. patent could be scaled down for application in such smaller sterilizers. However, it was found that, when the disclosed method was scaled down for use in smaller sterilizers, the smaller sterilizers cannot pass standardized efficacy testing. In this respect, all efficacy testing on low-temperature, vacuum sterilizers is done by performing half of the standard sterilization cycle. The sterilizer must be able to obtain a 106 lethality standard when only half of the operating cycle is performed. It was found, however, that scaled-down operating cycles could not demonstrate adequate kill in the abbreviated “half cycle” to meet existing standards.
Experimentation revealed that the first pulse of the cycle produced lower than expected sterilant concentration levels in the chamber. It is believed that the inability of the smaller sterilizers to utilize the scaled-down version of the established operating cycle for larger sterilizers was due to the difference in the surface area of the larger and smaller sterilizers. In other words, it is believed that the surface area to volume ratio of the chamber affects the performance of a conventional operating cycle used for larger sterilizers. In this respect, it is believed that initial injection of sterilant coats the inner surface of the chamber when the sterilant is first introduced into the chamber. This sterilant, in vapor form when introduced into the vacuum in the sterilization chamber, is believed to break down on contact with the surfaces within the chamber. It is possible that a catalytic reaction results with the metal within the chamber. Whatever the reason, merely scaling down existing methods of operating a sterilization cycle is not acceptable for smaller sterilization chambers.
The present invention overcomes this and other problems and provides a modified method of operating a sterilization cycle for use in smaller sterilizers.